Use same matcher for content source references (branches and tags) as is used for start paths

When the feature to select multiple start paths for a single content source was introduced, a new matching library was added that's more powerful than the one for selecting references (branches and tags). The pattern syntax for these two use cases should be aligned. In other words, the patterns for selecting references should be consistent with (and as powerful as) the pattern for selecting start paths.

The main difference is support for brace expressions: https://docs.antora.org/antora/latest/playbook/content-source-start-paths/#braces

This change has the potential to break existing patterns in certain circumstances if they rely on { as a literal character. However, that seems extremely unlikely.